Bellini -
Ranks of officers from junior to senior are:
2nd lieutenant, lieutenant, captain, major, lieutenant colonel, colonel, brigadier, major general, lieutenant general, general.
Soldier ranks:
private, lance corporal, corporal, sergeant, staff sergeant/colour sergeant, warrant officer class 2, warrant officer class 1.
CO = commanding officer. Rank of Lt Col and in charge of a whole regiment, battalion or battle group which on operations can be over 1000 people.
OC = Officer commanding a sub-unit of the above e.g. OC B Company. A company or squadron of men is usually somewhere between 100-200. A company/squadron is made up of several platoons or troops and is commanded by a Major. He has a 2IC (second in command) who is a Captain.
OC can also refer to a platoon/troop commander e.g. OC 3 platoon or OC mortar platoon but "the OC" as a title tends to refer to the Major in charge of the company or squadron.
A platoon or troop is usually about 30 men, commanded by a Lieutenant or sometimes a Captain. Platoons/troops are made up of usually 3 smaller sections of men (e.g. 2 Section in our girl). Each section is commanded by a corporal who is a junior NCO (non-commissioned officer).
I have no idea if this will make sense to anyone. (Or indeed if anyone cares but someone might!)
Marry into the army and you spend a whole lifetime deciphering irritating acronyms. And using the 24 hour clock in actual speech. Oh the shame... 